The priest was well-known for his missionary work among the young. MOSCOW, Nov 20 (Reuters) - A masked gunman entered a church and shot dead a Russian Orthodox priest well-known for his missionary work among the young, investigators said on Nov. 20.

The gunman approached priest Daniil Sysoyev, 34, in St Thomas Church in southern Moscow onNov. 19evening, asked his name and then opened fire with a pistol, a spokesman for the investigating committee of the Prosecutor-General's office said.

"The main theory is that religious motives are behind the crime," spokesman Anatoly Bagmet said in comments broadcast by Rossiya television.

Sysoyev died of his wounds on the way to hospital and his choirmaster was also injured in the attack, Bagmet said. He said other motives for the killing were also being investigated.

Sysoyev was heavily involved in missionary activities aimed at encouraging young people to choose the mainstream Orthodox Church. Russian news agencies said the priest had received threats via e-mail prior to the shooting.

Russia has seen a religious revival after the collapse of the Soviet Union and the dominant Orthodox Church has become an important political force with close ties to the Kremlin.

But Orthodox bishops have complained that Catholics and other Christian confessions are seeking to make converts on its territory.

Orthodox priests see the biggest threat coming from small religious groups such as Seventh-Day Adventists and the Unification Church, which they describe as "totalitarian cults".